Electrolytic plating solution, electrolytic plating method, and method for manufacturing semiconductor device

ABSTRACT

An electrolytic plating solution includes a polar solvent, copper sulfate dissolved in the polar solvent, an accelerator including a sulfur compound, and a reducing agent having a smaller molecular weight than the accelerator.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2008-76681 filed on Mar. 24, 2008, the entire contents of which, are incorporated herein by reference.

BACKGROUND

1. Field

The present invention generally relates to a semiconductor device and particularly to an electrolytic plating method, and a method for manufacturing a semiconductor device using the electrolytic plating method.

2. Description of Related Art

In today's ultrafine semiconductor integrated circuit devices, a multilayer wiring structure using a low resistance metal for its wiring pattern is used to interconnect a vast number of semiconductor elements formed on the substrate. Particularly, in a multilayer wiring structure using copper (Cu) for its wiring pattern, wiring grooves or via holes are previously formed in an interlayer insulating film made up of a silicon oxide film, or a material having a lower relative dielectric constant, the so-called low dielectric constant (low-k) material. A damascene method or a dual damascene method is generally used in which a Cu layer having low resistivity and high resistance to electromigration is formed to fill these via holes, and the surplus portions of the Cu layer are removed by chemical mechanical polishing (CMP).

In the damascene method or the dual damascene method, the surfaces of the wiring grooves or the via holes formed in the interlayer insulating film are covered with a barrier metal film made up of a high melting point metal or nitride thereof, typically Ta, TaN, or the like. By forming a thin Cu seed layer on the barrier metal film by a PVD method or a CVD method and performing electrolytic plating using such a Cu seed layer as an electrode, a Cu layer is formed to fill the wiring grooves or the via holes.

In the electrolytic plating step fox the Cu layer, generally, an electrolytic plating solution, such as an aqueous copper sulfate solution in which copper salt, such as copper sulfate, is dissolved in a polar solvent, such as water, is used. Generally, several types of additives are added in combination to the electrolytic plating solution to fill fine wiring grooves and via holes. For these additives, an accelerator (also referred to as a brightener) made up of a sulfur compound, and a suppressor (also referred to as an inhibitor) made up of a polymer having a molecular weight of about 1000 to 6000, such as polyethylene glycol and polypropylene glycol, are added to positively fill (bottom-up fill) the wiring grooves and the via holes from the bottom portions toward the upper portions. Further, a leveler made up of polymers having a molecular weight of more than 10000, many of which have a cyclic structure, may also be added. If either of the accelerator and the suppressor is absent, the desired bottom-up filling is not obtained.

FIGS. 1A to 1E depict the steps of forming a Cu wiring pattern by a typical damascene method, and FIG. 2 depicts an example of ideal bottom-up filling in forming such a Cu wiring pattern.

In FIG. 1A, recesses 12 constituting wiring grooves or via holes are formed in an insulating film 11. Next, depicted as FIG. 1B, a barrier metal film 13 typically made up of a high melting point metal, such as Ta and Ti, or conductive nitride thereof, such as TaN and TiN, is formed, in a shape conforming to the recesses 12, on the side wall surfaces and bottom, surfaces of the recesses 12.

Further, depicted as FIG. 1C, a Cu seed layer 14 is formed, in a shape conforming to the recesses 12, on the surface of the barrier metal film 13 by a PVD method or a CVD method. Further, depicted as FIG. 1D, a Cu layer 15 is formed to fill the recesses 12 by electrolytic plating using the Cu seed layer 14 as an electrode.

At the time, the previously described accelerator and suppressor are added to an electrolytic plating solution used. Thus, depicted as FIG. 2, filling with the Cu layer 15 occurs upwardly from the bottom portions of the recesses 12 (bottom-up filling).

Further, depicted as FIG. 1E, the unnecessary Cu layer 15 on the surface of the interlayer insulating film 11 is removed by a CMP method. Thus, a Cu wiring pattern 15A that has few voids and high resistance to stress migration and electromigration is obtained.

However, in recent semiconductor devices having an ultrafine multilayer wiring structure having a minimum via or groove diameter of 90 nm or less, a strongly acidic solution having a pH of 1 or less is generally used as an electrolytic plating solution. In this case, it is known that the problem that the thin Cu seed layer 14 is dissolved by the action of the plating solution occurs.

FIGS. 4A to 4C depict the state of the seed layer 14 depicted, in FIGS. 3A and 38, in the early stage of the electrolytic plating step depicted in FIG. 1D. However, FIGS, 4A to 4C are views in which the seed layer 14 covering the side wall surface of the recess 12 in the structure in FIG. 3A is seen in the direction depicted by the arrow in FIG. 3B. In FIGS. 4A to 4C, a thin Cu layer is formed on the seed layer 14 by a 10-second electrolytic plating step.

Referring to FIGS. 4A to 4C, in FIGS. 4A and 4B, the seed layer 14 is dissolved in the lower portion of the recess 12. Also, it is seen that in the view of FIG. 4(C), the seed layer 14 in the center portion is dissolved. In FIGS. 4A to 4C, a light portion seen in the lower portion of the recess 12 depicts a cross section of the seed layer 14 covering the bottom portion of the recess 12. It is seen that as a result of cleavage during sample making, the seed layer 14 is plastically deformed.

If the seed layer 14 is partly dissolved, in the structure in FIG. 1C, in this manner, the formation of the Cu layer 15 does not occur in portions lacking the seed layer 14 when electrolytic plating is performed in the step in FIG. 1D, using such a seed layer 14 as an electrode. Therefore, depicted as FIG. 5, defects, such as voids, occur in the Cu wiring pattern 15A filling the recesses 12.

Conventionally, in order to suppress the dissolution of the plating seed layer 14 in the electrolytic plating step, when the treated substrate is immersed in the electrolytic plating solution, voltage is previously applied to the treated substrate. On the other hand, when the treated substrate is immersed in the electrolytic plating solution, the treated substrate is immersed, obliquely tilted with respect to the liquid surface of the electrolytic plating solution to suppress the occurrence of bubbles. Then, when the treated substrate to which bias voltage is applied is immersed, obliquely tilted with respect to the liquid surface, in this manner, the deposition of a Cu layer immediately starts from the immersed portion. As a result, it is difficult to optimally control the formation of the Cu layer 15 depicted FIG. 1B. This problem is remarkable particularly in the manufacture of an ultrafine semiconductor device having a via diameter of 70 nm or less.

Also, conventionally, in order to suppress the dissolution of such a plating seed layer 14 in the electrolytic plating step, JP-A-2002-146585 proposes using a weakly acidic plating solution having a large pH value, or an alkaline plating solution. However, in such a technique, it is necessary to use a special plating solution. Also, optimal film formation conditions are limited. Therefore, it is difficult to generally use such a technique for the manufacture of an ultrafine semiconductor device.

Also, in order to suppress the dissolution of the above Cu seed layer in the electrolytic plating step, a technique of adding a high concentration of a suppressor to the electrolytic plating solution is proposed.

FIG. 6A is a view depicting the state of the Cu seed layer 14 when the formation of the Cu layer 15 is performed on the structure in FIG. 1C for about 10 seconds, using an electrolytic plating solution (a virgin makeup solution: VMS) made up of an aqueous copper sulfate solution containing neither an accelerator nor a suppressor.

FIG. 8B is a view depicting the state of the Cu seed layer 14 when similar electrolytic plating is performed on the structure in FIG. 1C for short time by adding to the VMS only disulfide propanesulfonic acid (SPS) generally used as an accelerator.

FIG. 6C is a view depicting the state of the Cu seed layer 14 when similar electrolytic plating is performed on the structure in FIG. 1C for short time by adding to the VMS only polyethylene glycol (PEG) generally used as a suppressor.

FIGS, 6A to 6C are views of the state of the side wail surface of the recess 12 seen, as in the FIGS. 4A to 4C.

Referring to FIGS. 6A to 6C, it is seen that in the case in FIG. 6A in which the VMS is used, the dissolution of the Cu seed layer 14 in the lower portion of the recess 12 is noted, and that in the case in FIG. 6B in which the accelerator is added to the VMS, the dissolution of the Cu seed layer 14 is further promoted. On the other hand, it is seen that in the case depicted in FIG. 6C in which only the suppressor is added, the dissolution of the Cu seed layer 14 decreases. However, the problem of dissolution is not completely solved even in the case in FIG. 6C. Then, it is considered that a high concentration of the suppressor is added into the electrolytic plating to solve only the problem of the dissolution of the Cu seed layer 14. However, when only the suppressor is added, the bottom-up filling of the recesses 12 with the Cu layer as previously described in FIG. 2 is impossible. Also, if the width of the recesses 12 is 70 nm or less, the dissolution of the Cu seed layer 14 in the bottom potions of the recesses 12 cannot be avoided even if the suppressor is added to the electrolytic plating solution, depicted as FIGS. 7A and 7B. However, FIGS. 7A and 78 depict, at different magnification, the state of the Cu seed layer 14 when the electrolytic plating of the Cu layer 15 is performed for short time in the step in FIG. 1D,

SUMMARY

According to an aspect of an embodiment, an electrolytic plating solution includes a polar solvent, copper sulfate dissolved in the polar solvent, an accelerator including a sulfur compound, and a reducing agent having a smaller molecular weight than the accelerator.

The object and advantages of the invention will be realised and attained by means of the elements and combinations particularly pointed out in the claims.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1E are views explaining the steps of forming a Cu wiring pattern by a damascene method;

FIG. 2 is a view showing an example of ideal bottom-up filling;

FIGS. 3A and 3B are views explaining the problem;

FIGS. 4A to 4C are views explaining the problem;

FIG. 5 is a view explaining the problem;

FIGS. 6A to 6C are views explaining the problem;

FIGS. 7A and 7B are views explaining the problem;

FIG. 8 is a view showing the configuration of an electrolytic plating apparatus used in an embodiment;

FIGS. 9A to 9D are views explaining experiment performed in a first embodiment;

FIGS. 10A and 10B are views showing the result of the experiment;

FIGS. 11A and 11B are views showing the interpretation of the experiment;

FIG. 12 is a view showing the interpretation of the experiment;

FIG. 13 is a view further explaining the experiment;

FIG. 14 is a view further explaining the experiment;

FIGS. 15A to 15E are views explaining the steps of forming a Cu wiring pattern by a damascene method according to a second embodiment;

FIGS. 16A to 16L are views explaining the steps of forming a Cu wiring pattern by a dual damascene method according to a third embodiment; and

FIG. 17 is a view showing the configuration of a semiconductor device according to a fourth, embodiment.

DESCRIPTION OF EMBODIMENTS First Embodiment

The effect of the accelerator and the suppressor on the problem of the dissolution of the Cu seed layer 14 previously described has been examined. As a result, it has been found that when a compound having a smaller molecular weight than a compound used as the accelerator, for example, glucose is further added as a reducing agent to the electrolytic plating solution, the dissolution of the Cu seed layer 14 is very effectively suppressed.

FIG. 8 shows the schematic configuration of an electrolytic plating apparatus 1 used in experiment, and FIGS. 9A to 9D show the outline of the experiment performed by the inventor.

First, FIG. 8 is referred to.

The electrolytic plating apparatus 1 has a container 2 in which an anode 2B is held in an electrolyte 2A, and a treated substrate W is immersed in the electrolyte 2A.

A tank 3 is connected to the container 2 via pipes 3A and 38, and the electrolyte 2A is circulated between the container 2 and the tank 3 through the pipes 3A and 38.

Further, a VMS supplying unit 4A, an accelerator supplying unit 4B, a suppressor supplying unit 4C, a leveler supplying unit 4D, and a reducing agent supplying unit 4E are connected to the tank 3 via respective lines. Also, a concentration measurement apparatus 5 that measures the concentration of the electrolyte 2A in the tank 3 is coupled to the tank 3. Further, in electrolytic plating treatment, a direct current power source DC is connected to the treated substrate W and the anode 28.

Referring to FIG. 9A, recesses 22 constituting wiring grooves or via holes are formed, with a width and depth of 70 nm, in an insulating film 21. Further, a barrier metal film 23 made up of a Ta film is formed, in a shape conforming to the recesses 22 and with a film thickness of 5 to 6 nm, on the side wall surfaces and bottom surfaces of the recesses 22, as shown in FIG. 9B. Further, as shown in FIG. 9C, a Cu seed layer 24 is formed, in a shape conforming to the recesses 22 and with a film thickness of 40 to 100 nm, on the surface of the barrier metal film 23 by a PVD method.

Further, in a step in FIG. 90, electrolytic plating using the Cu seed layer 24 as an electrode is performed for short time, typically 10 seconds, using the electrolytic plating apparatus 1. Thus, a Cu layer 25 is formed, with a film thickness of about 10 nm, on the surface of the Cu seed layer 24. By forming the thin Cu layer 25 on the surface of the Cu seed layer 24 in this manner, defects in the Cu seed layer 24 can be more clearly detected.

In Example 1, as the electrolyte 2A, an aqueous copper sulfate solution containing Cu ions at a concentration of 60 g/L, also sulfuric acid (H₂SO₄) at a concentration of 10 g/L, and further chlorine (Cl) at a concentration of 50 ppm was made as a VMS. At the time, in Example 1, further, disulfide propanesulfonic acid (SPS) having the chemical formula HO₃S—CH₂CH₂CH₂—S—S—CH₂CH₂CH₂—SO₃H and a molecular weight M of 310 was added to the VMS as an accelerator at a concentration of 20 mg/L, and also polyethylene glycol (PEG) having a molecular weight of 400, 2000, and 6000 was added as a suppressor to make three types of electrolytic plating solutions in which the polymerization degree of the suppressor was different. On the other hand, in the example of Example 1, a leveler was not used because the embedding of the Cu layer in the recesses 22 was not much affected.

Further, in Example 1, D (+) glucose having a molecular weight of 180 was added to the electrolyte 2A as the reducing agent at a rate of 10 to 20 ppm.

FIGS. 10A and 108 show views of samples, in which the Cu layer 25 was formed, with a film thickness of about 10 nm, on the structure in FIG. 9C in the electrolytic plating apparatus 1 in FIG. 8, observed in the direction of the arrow as shown in FIG. 9D. Here, the sample in FIG. 10A shows a control standard in which glucose was not added, while the sample in FIG. 10B shows the sample of Example 1 in which glucose was added. However, in either of the samples in FIGS. 10A and 10B, polyethylene glycol having a molecular weight of 2000 was added as a suppressor at a rate of 300 g/L.

Also, in the experiment in FIGS. 10A and 10B, in the apparatus 1 in FIG. 8, bias voltage was not applied when the treated substrate W was immersed in the electrolytic plating solution 2A, and after the treated substrate w was immersed, energization was performed at a current density of 5 to 10 mA/cm². The temperature of the plating solution was set at 25° C. (ordinary temperature; room temperature).

When FIGS. 10A and 10B are compared, it is seen that the dissolution of the Cu seed layer 24 occurred in a manner similar to that previously described in FIGS. 4A to 4C, when glucose was not added, while the dissolution of such a Cu seed layer 24 completely stopped by adding glucose.

The result in FIGS. 10A and 10B suggests the following mechanism for the dissolution of the Cu seed layer.

As schematically shown in FIG. 11A, when a reducing agent, such as glucose, is not included in the electrolytic plating solution 2A, the Cu seed layer 24 is oxidized by dissolved oxygen in the electrolytic plating solution 2A, and formed copper oxide, such as CuO or Cu₂O, is dissolved by the electrolytic plating solution 2A. At the time, when an accelerator is included in the electrolytic plating solution 2A, the oxidation of the Cu seed layer 24 is promoted, and as a result, the dissolution of the Cu seed layer 24 is promoted.

However, when a reducing agent, such as glucose, is present in the electrolytic plating solution 2A, copper oxide formed by dissolved oxygen in the electrolytic plating solution is immediately reduced to Cu, as schematically shown in FIG. 11B. Therefore, even if an accelerator is included in the electrolytic plating solution 2A, the dissolution of the Cu seed layer 24 is suppressed.

In view of such a mechanism, it is considered that the reducing agent is not limited to glucose and may be saccharides, aldehyde groups, or ketone groups that include an aldehyde group or a ketone group and exhibit the action of reduction.

Then, from the consideration in FIGS. 11A and 11B, it is considered that the dissolution of the Cu seed layer 24 by the electrolytic plating solution is suppressed by adding the reducing agent, in addition to the accelerator, into the electrolytic plating solution 2A.

However, when the case where a fine recess, for example, the recess 22 having a minimum line width W of 70 nm or less shown in FIG. 12 is filled by the electrolytic plating of a Cu layer is considered, it is desirable that in the above-described mechanism, the reducing agent is transported to the bottom portion 22A of the recess 22, which is surrounded by the broken line, with efficiency equal to or higher than that of the accelerator. For this, it is desirable that the reducing agent is a compound having a molecular weight equal to or less than that of the accelerator. In the example in FIG. 12, a lower-layer insulating film 31 is formed under the insulating film 21 via a barrier metal film 32. The accelerator SPS used in this example has a molecular weight of about 310. Therefore, it is desirable that the reducing agent has a molecular weight of, for example, 300 or less. Glucose has a molecular weight of about 180 and satisfies the above conditions.

Such a reducing agent having an aldehyde group or a ketone group and having a molecular weight of 300 or less includes, in addition to glucose having a molecular weight of 180, monosaccharides, such as glyceraldehyde having a molecular weight of 90, erythrose having a molecular weight of 120, threose having a molecular weight of 120, ribose having a molecular weight of 150, arabinose having a molecular weight of 150, xylose having a molecular weight of 150, lyxose having a molecular weight of 150, allose having a molecular weight of 180, altrose having a molecular weight of 180, mannose having a molecular weight of 180, gulose having a molecular weight of 180, idose having a molecular weight of 180, galactose having a molecular weight of 180, and talose having a molecular weight of 180.

Further, the reducing agent includes aldehyde groups, such as formaldehyde having a molecular weight of 30, acetaldehyde having a molecular weight of 44, propionaldehyde having a molecular weight of 58, vinyl aldehyde having a molecular weight of 55, benzaldehyde having a molecular weight of 106, cinnamaldehyde having a molecular weight of 132, and perillaldehyde having a molecular weight of 150, and further ketone groups, such as acetone having a molecular weight of 59, methyl ethyl ketone having a molecular weight of 72, and diethyl ketone having a molecular weight of 86.

Particularly when mercaptopropanesulfonic acid (MPS) having a molecular weight of 155 is used as the accelerator, instead of SPS, effect similar to that previously described can be obtained by using the above reducing agents having a molecular weight of 155 or less.

Next, in order to confirm the action and effect of the above reducing agents, polyethylene glycol that does not have reduction properties was added, instead of the glucose, to the electrolytic plating solution 27A at various molecular weights (400, 2000, and 6000) and concentrations (300 mg/L and 3000 mg/L), and whether the effect of suppressing the dissolution of the Cu seed layer 24 occurred or not was examined by experiment under the same conditions as the previous experiment in FIGS. 10A and 10B. The result is shown in FIG. 13.

Referring to FIG. 13, it is seen that remarkable dissolution occurred in the Cu seed layer 2 4 in any of the cases.

According to FIG. 13, it is concluded that even if simply an additive having a smaller molecular weight than the accelerator is added to the electrolytic plating solution 2A, the effect of suppressing the dissolution of the Cu seed layer 24 that is previously obtained in FIGS. 10A and 10B is not obtained if the additive does not exhibit reduction action.

Further, in order to confirm the action and effect of the above reducing agents, the electrolytic plating solution 2A, in which polyethylene glycol having a molecular weight of 2000 or 6000 was used as a suppressor, and to which polyethylene glycol having a molecular weight of 200 was further added, instead of the reducing agent, was used, and whether the effect of suppressing the dissolution of the Cu seed layer 24 occurred or not was examined by experiment under the same conditions as the previous experiment in FIGS. 10A and 10B. The result is shown in FIG. 14.

FIG. 14A shows a control standard in which the polyethylene glycol having a molecular weight of 200 was not added, and FIG. 14B shows an example in which the polyethylene glycol having a molecular weight of 200 was added.

Referring to FIGS. 14A and 14B, it is shown that even if polyethylene glycol having a molecular weight of 200 was added, holes were formed in the Cu seed layer 24, and dissolution by the electrolytic plating solution could not be sufficiently suppressed,

From the above, the findings are shown that the problem, of the dissolution of the Cu seed layer by the electrolytic plating solution to which the accelerator is added can be solved by further adding a reducing agent to the electrolytic plating solution and, at the time, selecting and using as the reducing agent a reducing agent having a molecular weight equal to or less than the molecular weight of the accelerator.

When the reducing agent is added to the electrolytic plating solution in this manner to perform, for example, the electrolytic plating step in FIG. 9D, using the electrolytic plating apparatus 1 in FIG. 8, it is not necessary to perform voltage application to the treated substrate W before immersion into the electrolytic plating solution 2A, which is conventionally performed to suppress the dissolution of the Cu seed layer 24. In other words, it is possible to start the energization of the treated substrate W after the treated substrate w is immersed in the electrolytic plating solution 2A. As a result, it is possible to perform the filling of the recesses 22 with the Cu layer 25 under optimal current conditions. As a result, it is possible to form fine via holes or wiring grooves having a minimum line width of 70 nm or less without defects by the bottom-up process as shown in FIG. 2.

In the electrolytic plating solution 2A in this example, the solvent that dissolves copper sulfate is not limited to water, and other polar solvents, for example, alcohols, such as methanol and ethanol, cyclic carbonates, such as ethylene carbonate and propylene carbonate, and linear carbonates, such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate, or mixed solvents thereof can also be used.

Second Embodiment

FIGS. 15A to 15E show a method for forming a Cu wiring pattern according to a second embodiment.

FIG. 15A is referred to.

Recesses 42 constituting wiring grooves or via holes are formed, with a width and depth of 70 nm, in an insulating film 41. A barrier metal film 43 made up of a Ta film is formed, in a shape conforming to the recesses 42 and with a film thickness of, for example, 5 to 6 nm, on the side wall surfaces and bottom surfaces of the recesses 42, as shown in FIG. 15B. Further, as shown in FIG. 15C, a Cu seed layer 44 is formed, in a shape conforming to the recesses 42 and with a film thickness of 40 to 100 nm, on the surface of the barrier metal film 43 by a PVD method,

Further, in a step in FIG. 15D, electrolytic plating using the Cu seed layer 44 as an electrode is performed in the electrolytic plating apparatus 1 to bottom-up fill the recesses 42 from the surface of the Cu seed layer 44 with a Cu layer 45. At the time, as the electrolytic plating solution 2A, one in which SPS as an accelerator, polyethylene glycol as a suppressor, and further glucose as a reducing agent are added to an aqueous copper sulfate solution, as described in the previous embodiment, is used.

Further, in a step in FIG. 15E, by removing the unnecessary Cu layer 45 on the surface of the interlayer insulating film 41 by a CMP method, a Cu wiring pattern 45A that has few voids and therefore has high resistance to stress migration and electromigration is obtained.

In this embodiment, glucose is added as a reducing agent to the electrolytic plating solution 2A. Therefore, even if an accelerator, such as SPS, is added to the electrolytic plating solution 2A, the dissolution of the Cu seed layer 44 is suppressed. As a result, in the electrolytic plating step in FIG. 15D, the recesses 42 can be bottom-up filled with the Cu layer 45, and the occurrence of defects, such as voids, in the Cu wiring pattern 45A can be effectively suppressed.

Also, as previously described, when, the electrolytic plating step in FIG. 15D is performed using the electrolytic plating apparatus 1 in FIG. 8, it is not necessary to perform voltage application to the treated substrate W before immersion into the electrolytic plating solution 2A, which is conventionally performed to suppress the dissolution of the Cu seed layer 44. In other words, it is possible to start the energization of the treated substrate W after the treated substrate W is immersed in the electrolytic plating solution 2A. As a result, it is possible to perform the filling of the recesses 42 with the Cu layer 45 under optimal current conditions. Therefore, it is possible to form fine via holes or wiring grooves having a minimum line width of 70 nm or less without defects by the bottom-up process as shown in FIG. 2.

In this embodiment, for example, a leveler commercially available from ATMI under the trade name Viaform Leveler may be added, as required, to the electrolytic plating solution 2A.

Third Embodiment

Next, the steps of manufacturing a semiconductor device having a multilayer wiring structure according to a third embodiment will be described referring to FIG. 16A to FIG. 16L.

Referring to FIG. 16A, an interlayer insulating film 303 made up of SiO₂ or the like is formed on an insulating film 301 on a silicon substrate (not shown) via a SIN film 302. A resist pattern R1 corresponding to the desired wiring pattern is formed on the interlayer insulating film 303.

Next, in a step in FIG. 16B, the interlayer insulating film 303 is patterned using the resist pattern R1 as a mask. As a result, wiring grooves corresponding to the desired wiring patterning are formed in the interlayer insulating film 303. Further, the interlayer insulating film 303 patterned in this manner is covered with a Ta barrier metal film 304, and then, the steps in FIGS. 15A to 15D are executed. Thus, a copper layer CL1 is formed by the electrolytic plating method so as to fill the wiring grooves. In this electrolytic plating method, an electrolytic plating solution in which SPS as an accelerator, polyethylene glycol as a suppressor, and glucose as a reducing agent are added to an aqueous copper sulfate solution is used.

Further, in a step in FIG. 16C, the copper layer CL1 and the barrier metal film 304 under the copper layer CL1 are polished and removed by a CMP method until the surface of the interlayer insulating film 303 is exposed. Further, a next interlayer insulating film 306 made up of SiO₂ or the like is formed on the structure formed in this manner, via a SiN barrier film CL1.

In the step in FIG. 16C, further, a next interlayer insulating film 308 made up of SiO₂ or the like is formed on the interlayer insulating film 306 via a SiN barrier film 307. Further, a resist pattern R2 corresponding to the desired contact hole is formed on the interlayer insulating film 308.

Next, in a step in FIG. 16D, the interlayer insulating film 303, the barrier film 307, and the interlayer insulating film 306 are sequentially patterned using the resist pattern R2 as a mask to form a contact hole 308C in such a manner that the SiN barrier film 305 is exposed in the bottom portion. Then, a non-photosensitive resin film is applied to fill the contact hole 308C with the resin film. Further, the resin film on the interlayer insulating film 308 is dissolved and removed to leave a resin protective portion 308R in the contact hole 308C.

Further, in the step in FIG. 16D, a resist pattern R3 corresponding to wiring grooves desired to be formed in the interlayer insulating film 308 is formed on the interlayer insulating film 308.

Next, in a step in FIG. 16E, with the inner wall surface of the contact hole 308C protected by the resin protective portion 308R, the interlayer insulating film 308 is patterned using the resist pattern R3 as a mask until the SiN barrier film 307 is exposed. Thus, the desired wiring grooves 308G are formed in the interlayer insulating film 308.

Further, in the step in FIG. 16E, after the interlayer insulating film 308 is patterned, the resin protective portion 308R is removed by an ashing process.

Further, in a step in FIG. 16F, using the interlayer insulating film 308 as a self-alignment mask, the SiN barrier films 307 and 305 are respectively removed from, the bottom, portions of the wiring grooves 308G and the contact hole 308C. Further, the surface of the structure obtained in this manner is covered with a Ta barrier metal film 309, and then, the previous steps in FIGS. 15A to 15D are executed for a copper layer CL2 so that the copper layer CL2 fills the contact hole 308C and the wiring grooves 308G. Thus, the copper layer CL2 is formed by the electrolytic plating method using an electrolytic plating solution in which SPS as an accelerator, polyethylene glycol as a suppressor, and glucose as a reducing agent are added to an aqueous copper sulfate solution.

Next, in a step in FIG. 16G, the copper layer CL2 and the Ta barrier metal film 309 under the copper layer CL2 in FIG. 10F are removed by the CMP method until the surface of the interlayer insulating film 308 is exposed. Further, a SiN barrier film 311, and an interlayer insulating film 312 made up of SiO₂ or the like, are formed on the structure obtained in this manner.

Further, in the step in FIG. 16G, a resist pattern R4 corresponding to via holes desired to be formed in the interlayer insulating film 312 is formed on the interlayer insulating film 312.

Further, in a step in FIG. 16H, the interlayer insulating film 312 and the SiN barrier film 311 under the interlayer insulating film 312 are patterned using the resist pattern R4 as a mask. As a result, the desired via holes 312V are formed in the interlayer insulating film 312.

Further, in a step in FIG. 16I, for the structure in FIG. 16H, a barrier metal layer 313 made up of a TaN film is formed on the interlayer insulating film 312 by reactive sputtering so as to continuously cover the side wall surfaces and bottom surfaces of the via holes 312V. Further, a TiN barrier metal film 314 is formed on the TaN barrier metal film 313 also by reactive sputtering. Further, in a step in FIG. 16J, a tungsten film 315 is formed on the structure in FIG. 16I by the CVD method so that the tungsten film 315 fills the via holes 312V.

Further, in a step in FIG. 16K, the tungsten film 315, and the TiN film 314 and the TaN 313 under the tungsten film 315 are polished and removed by the CMP method, until the surface of the interlayer insulating film 312 is exposed, to form tungsten via plugs 315W in the via holes 312V.

Further, in the step in FIG. 16K, a conductor film 316 b made up of aluminum or an aluminum-copper alloy is formed on the interlayer insulating film 312 via a TiN barrier metal film 316 a. Further, another TiN barrier metal film 316 c is formed on the conductor film 316 b. The conductor film 316 b, together with the TiN barrier metal films 316 a and 316 c, forms a wiring layer 316.

In the state in FIG. 16K, a resist pattern R5 corresponding to a wiring pattern desired to be further formed is formed on the wiring layer 316. Further, in a step in FIG. 16L, the wiring layer 316 is patterned by dry etching or the like, using the resist pattern R5 as a mask, so that wiring patterns 316A and 316B are formed on the tungsten plugs 315W.

Further, in the step in FIG. 16L, an interlayer insulating film 317 of SiO₂ or the like is deposited on the interlayer insulating film 312 so as to cover the wiring patterns 316A and 316B, and a passivation film 318 of SiN or the like is formed on the surface of the interlayer insulating film 317.

In this embodiment, the electrolytic, plating step for the Cu layer CL1 or CL2 in FIG. 16B or FIG. 16F is executed using an electrolytic plating solution made up of an aqueous copper sulfate solution to which SPS as an accelerator, polyethylene glycol as a suppressor, and further glucose as a reducing agent are added, as previously described in FIGS. 15A to 15D. Thus, the wiring grooves can be bottom-up filled with the Cu layer CL1 or CL2 without dissolving the Cu seed layer not shown. As a result, the occurrence of defects, such as voids, can be effectively suppressed.

Also in this embodiment, when the electrolytic plating step in FIG. 16B or FIG. 16F is performed using the electrolytic plating apparatus 1 in FIG. 8, it is not necessary to perform voltage application to the treated substrate W before immersion into the electrolytic plating solution 2A, which is conventionally performed to suppress the dissolution of the Cu seed layer. Therefore, it is possible to start the energization of the treated substrate W after the treated substrate W is immersed in the electrolytic plating solution 2A. As a result, it is possible to perform the filling of the recesses with the Cu layer CL1 or CL2 under optimal current conditions. Thus, it is possible to form fine via holes or wiring grooves having a minimum line width of 70 nm or less without defects by the bottom-up process as shown in FIG. 2.

Fourth Embodiment

FIG. 17 is a view showing the configuration of a semiconductor device having a multilayer wiring structure formed in this manner, according to a fourth embodiment.

Referring to FIG. 17, an element region 401A is defined on a silicon substrate 401 by a STI structure 402. In the element region 401A, a gate electrode 403 is formed on the silicon substrate 401 via a gate insulating film 403A.

A side wall insulating film is formed on both side wall surfaces of the gate electrode 403. Further, in the silicon substrate 401, LDD regions 401 a and 401 b are formed on both sides of the gate electrode 403. Also, in the silicon substrate 401, diffusion regions 401 c and 401 d forming a source region or a drain region are formed outside the side wail insulating films. Also, the surface of the silicon substrate 401 is uniformly covered with a SiN film 404, except the gate electrode 403 and portions where its side wall insulating films are formed.

Further, an interlayer insulating film 405 made up of SiO₂ or the like is formed on the SiN film 404 so as to cover the gate electrode 403 and the side wail insulating films. Contact holes 405A and 405B exposing the diffusion regions 401 c and 401 d are formed in the interlayer insulating film 405.

The side wall surfaces and bottom surfaces of the contact holes 405A and 4053 are covered with a barrier metal film 406 in which a TaN film and a TiN film are laminated. Further, the contact holes 405A and 405B are filled with tungsten plugs 407 via the barrier metal film.

Further, copper wiring structures 408, 409, and 410 in which copper wiring patterns are embedded in an interlayer insulating film are sequentially formed on the interlayer insulating film 405 by the damascene method or dual damascene method as described in the previous example. Conductive plugs 413 made up of tungsten are formed in via holes, whose side wall surfaces and bottom surfaces are continuously covered with a barrier metal film 412 made up of a conductive nitride film in which a TaN film and a TiN film are laminated, in an interlayer insulating film 411 on the copper wiring structure 410.

Further, wiring patterns 414A and 414B having a configuration in which a conductor film made up of aluminum or an aluminum alloy is sandwiched between TiN barrier metal films are formed on the interlayer insulating film 411. Further, an interlayer insulating film 415 is formed on the interlayer insulating film 411 so as to cover the wiring patterns 414A and 414B.

Further, the surface of the interlayer insulating film 415 is covered with a passivation film 416 made up of SiN or the like.

The problem of dissolution occurring in the copper seed layer used as an electrode in the electrolytic plating step for the copper layer, using the electrolytic plating solution, is effectively suppressed by the reducing agent having a smaller molecular weight than the accelerator that is added to the electrolytic plating solution. As a result, it is possible to sequentially fill fine recesses with the copper layer from the lower portions to the upper portions,

The foregoing is considered as illustrative only of the principles of the present invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and applications shown and described, and accordingly, all suitable modifications and equivalents may be regarded as failing within the scope of the invention in the appended claims and their equivalents. 

1. An electrolytic plating solution, comprising: a polar solvent, copper sulfate dissolved in the polar solvent, an accelerator including a sulfur compound, and a reducing agent having a smaller molecular weight than the accelerator.
 2. The electrolytic plating solution according to claim 1, wherein the reducing agent is a compound having a water-soluble aldehyde group or ketone group.
 3. The electrolytic plating solution according to claim 1, wherein the reducing agent has a molecular weight of 300 or less.
 4. The electrolytic plating solution according to claim 1, wherein the reducing agent is a monosaccharide.
 5. The electrolytic plating solution according to claim 1, wherein the reducing agent comprises glucose.
 6. The electrolytic plating solution according to claim 1, wherein the accelerator comprises disulfide propanesulfonic acid.
 7. The electrolytic plating solution according to claim 1, further comprising polyethylene glycol as a suppressor.
 8. An electrolytic plating method, comprising: immersing a treated substrate, on which a copper seed layer is formed, in an electrolytic plating solution, and depositing a copper layer on the treated substrate immersed in the electrolytic plating solution by electrolytic plating, wherein the electrolytic plating solution comprises: a polar solvent, copper sulfate dissolved in the polar solvent, an accelerator including a sulfur compound, and a reducing agent having a smaller molecular weight than the accelerator.
 9. The electrolytic plating method according to claim 8, wherein energization is started after the treated substrate is immersed in the electrolytic plating solution.
 10. A method for manufacturing a semiconductor device, comprising: forming a recess in an insulating film on a treated substrate, forming a barrier metal film, in a shape conforming to a shape of the recess, on the insulating film so as to continuously cover a side wall surface and bottom surface of the recess, forming a copper seed layer, in a shape conforming to the shape of the recess, on the insulating film, covering the barrier metal film, filling the recess with a copper layer by electrolytic plating using the copper seed layer as an electrode, and removing the copper layer on the insulating film by a chemical mechanical polishing method until a surface of the insulating film is exposed, wherein an electrolytic plating solution used for forming the copper layer comprises: a polar solvent, copper sulfate dissolved in the polar solvent, an accelerator including a sulfur compound, and a reducing agent having a smaller molecular weight than the accelerator.
 11. The method for manufacturing a semiconductor device according to claim 10, wherein the electrolytic plating method comprises: immersing the treated substrate in the electrolytic plating solution, and performing energization in the electrolytic plating solution, using the copper seed layer as an electrode, wherein the energization is started after the treated substrate is immersed in the electrolytic plating solution. 